The objective of this proposal is to elucidate the mechanism(s) which controls the biosynthesis of the histidine-rich protein (HRP) in Plasmodium lophurae and the knob protein (KP) of Plasmodium falciparum. These studies may lead to a better understanding of parasite differentiation at the molecular level. In addition, since these proteins may have important biological and immunological roles in the survival of the parasites in their hosts, these studies may lead to new therapeutic approaches to the disease. The immediate aims will be to: 1) Prepare an HRP cDNA containing plasmid probe and determine the sequence of the HRP; 2) Determine the control of HRP biosynthesis during the growth and differentiation of P. lophurae; 3) Determine the degree of homology between the HRP of P. lophurae and the knob protein of P. falciparum. The HRP is a unique protein containing over 70 percent histidine. Due to the unusual chemical properties of the HRP, it is difficult to apply most standard biochemical and immunological techniques to its study. Therefore, in the present proposal, the tools of molecular biology will be used to study the structure and expression of the HRP gene(s). An HRP cDNA containing plasmid will be isolated from a P. lophurae cDNA library using a synthetic polyhistidine oligonucleotide probe. The inserted cDNA will be sequenced in order to deduce the amino acid sequence of the HRP. This probe will then be used to determine the pool size of the HRP mRNA, the presence or absence of HRP HnRNA precursor molecules, and the structure and organization of the HRP gene(s). Cell-free translation, cell-fractionation techniques, cDNA cloning, RNA-DNA hybridization kinetics, and RNA and DNA blotting technology will be employed in these studies. The degree of homology between the HRP and KP will also be determined using the techniques listed above. The results of these studies will be used to determine the relative contributions of transcriptional and translational control in HRP and KP biosynthesis.